Fuel cell stack column including stress-relief components

ABSTRACT

A fuel cell column includes termination plates, fuel cell stacks disposed between the termination plates, and fuel manifolds disposed between the fuel cell stacks. The fuel cell stacks include fuel cells, interconnects disposed between the fuel cells, and end plates disposed on opposing ends of the fuel cell stacks. At least one of the termination plates and/or the fuel manifold may include first and second separate pieces separated by an expansion zone. The fuel cell stack may also include one or more buffer layers and/or seals configured to reduce CTE differences of components of the fuel cell stack.

FIELD

Aspects of the present disclosure relate generally to a fuel cell stackcolumn including stress-relief components.

BACKGROUND

U.S. application Ser. No. 11/656,563, filed on Jan. 23, 2007 andpublished as US published application 2007/0196704 A1 and incorporatedherein by reference in its entirety, describes a fuel cell system inwhich the solid oxide fuel cell (SOFC) stacks are located on a base, asshown in FIG. 1. Wedge shaped ceramic side baffles 220 (e.g., having anon-uniform thickness and a roughly triangular cross sectional shape inthe horizontal direction) are located between adjacent fuel cell stacks14 (or columns of fuel cell stacks). The baffles 220 serve to direct thecathode feed into the cathode flow paths and to fill the space betweenadjacent stacks so that the cathode feed passes through each of thestacks 14, rather than bypassing around the longitudinal sides of thestacks 14. The baffles 220 are held in place by tie rods 222 that passthrough closely fitting bores 224 centrally located in each of thebaffles 220. Preferably, the baffles 220 are electrically non-conductiveand made as one unitary piece from a suitable ceramic material. FIG. 1also shows fuel distribution manifolds between the stacks in the stackcolumn and fuel inlet and exhaust conduits connected to the manifolds.

In this prior art system, the SOFC stacks maintain a compressive load.The compressive load is maintained by upper pressure plate 230, tie rods222, lower pressure plate 90 and a compression spring assembly locatedbelow the lower pressure plate 90. The compression spring assemblyapplies a load directly to the lower pressure plate 90 and to the upperpressure plate 230 via the tie rods 222. The bores or feed-throughs 224through the baffles 220 act as heat sinks and thereby decrease thesystem efficiency.

In an alternative embodiment, the load is transmitted through the base239 as this is the only zero datum of the system. Penetrations orfeed-throughs through the base 239 are used in order to pull therequired load from the base 239.

SUMMARY

According to various embodiments, provided is a fuel cell stack columncomprising: first and second termination plates; and at least one fuelcell stack disposed between the first and second termination plates,wherein at least one of the first and second termination platescomprises first and second pieces separated by an expansion zone.

According to various embodiments, provided is fuel cell stack columncomprising: first and second fuel cell stacks; and a fuel manifoldcomprising a main body disposed between the first and second fuel cellstacks, the main body comprising first and second pieces separated by anexpansion zone.

According to various embodiments, provided is a fuel cell stack columncomprising: termination plates; fuel cell stacks disposed between thetermination plates; a fuel manifold comprising a main body disposedbetween at least two adjacent fuel cell stacks; and at least one of: afirst buffer layer disposed between the fuel manifold and an adjacentfuel cell stack; and a second buffer layer disposed between one of thetermination plates and the adjacent fuel cell stack. Each fuel cellstack comprises: fuel cells; interconnects disposed between the fuelcells; and end plates disposed on opposing ends of the fuel cell stack.The coefficient of thermal expansion (CTE) of the first buffer layer isbetween the CTE of the end plates and the CTE of the fuel manifold, andthe CTE of the second buffer layer between the CTE of the end plates andthe CTE of the termination plates.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate exemplary embodiments of theinvention, and together with the description serve to explain theprinciples of the invention.

FIG. 1 illustrates a three dimensional view of a conventional fuel cellassembly.

FIG. 2 illustrates a three dimensional view of a fuel cell stackassembly according to an exemplary embodiment of the present disclosure.

FIG. 3 illustrates a three dimensional view of a fuel cell stackassembly according to an exemplary embodiment of the present disclosure.

FIG. 4 illustrates an exploded view of a compression assembly accordingto an exemplary embodiment of the present disclosure.

FIG. 5 illustrates a cross-sectional view of a compression assemblyaccording to an exemplary embodiment of the present disclosure.

FIGS. 6A and 6B are schematic front views of a fuel cell stack assemblyat 20° C. and 700° C., respectively.

FIG. 7 is a schematic front view of a fuel cell stack assembly,according to various embodiments of the present disclosure.

FIG. 8A is a top plan view of a modified termination plate according tovarious embodiments of the present disclosure, and FIG. 8B is a top planview of a general termination plate.

FIG. 9 is an exploded perspective view of a portion of a fuel cell stackassembly, according to various embodiments of the present disclosure.

FIG. 10 is an exploded perspective view of a fuel cell stack assembly,according to various embodiments of the present disclosure.

FIG. 11 is a front schematic view of a fuel cell stack assembly,according to various embodiments of the present disclosure.

FIG. 12 is an exploded perspective view of a fuel cell stack assembly,according to various embodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure is described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure is thorough, and willfully convey the scope of the invention to those skilled in the art. Inthe drawings, the size and relative sizes of layers and regions may beexaggerated for clarity. Like reference numerals in the drawings denotelike elements.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, it can bedirectly on or directly connected to the other element or layer, orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on” or “directly connected to”another element or layer, there are no intervening elements or layerspresent. It will be understood that for the purposes of this disclosure,“at least one of X, Y, and Z” can be construed as X only, Y only, Zonly, or any combination of two or more items X, Y, and Z (e.g., XYZ,XYY, YZ, ZZ).

The bores or feed-throughs 224 of the system of FIG. 1 decrease thesystem efficiency because they create heat sinks. The bores 224 can beeliminated and a compressive load applied to the fuel cell stacks 14 byredesigning the baffles 220. By applying the compressive stress with thebaffles themselves, the tie rods 222 can be eliminated, and thus, thebores 224 can be eliminated. Thus, in one embodiment, the baffles lackbore holes that extend vertically through the baffles and tie rodslocated in the holes.

FIG. 2 illustrates a fuel cell stack assembly 200 according to variousembodiments of the present disclosure. Referring to FIG. 2, the fuelcell stack assembly 200 includes a fuel cell stack column 140, sidebaffles 220 disposed on opposing sides of the column 140, a lower block503, and a compression assembly 600 including an upper block 603. Thecolumn includes three fuel cell stacks 14, fuel manifolds 204 disposedbetween the fuel cell stacks 14, and termination plates 27 disposed onopposing ends of the column 140. The fuel cell stacks 14 include aplurality of fuel cells stacked upon one another and separated byinterconnects. A plurality of the fuel cell stack assemblies 200 may beattached to a base 239, as shown in FIG. 1.

An exemplary fuel manifold 204 is described in the U.S. application Ser.No. 11/656,563 noted above. Any number of fuel manifolds 204 may beprovided between adjacent end plates of adjacent fuel cells of the fuelcell stacks 14, as desired.

The side baffles 220 connect the upper block 603 of the compressionassembly 600 and the lower block 503. The side baffles 220, thecompression assembly 600, and the lower block 503 may be collectivelyreferred to as a “stack housing”. The stack housing is configured toapply a compressive load to the column 140. The configuration of thestack housing eliminates costly feed-throughs and resulting tie rod heatsinks and uses the same part (i.e., side baffle 220) for two purposes:to place the load on the stacks 14 and to direct the cathode feed flowstream (e.g., for a ring shaped arrangement of stacks shown in FIG. 1,the cathode inlet stream, such as air or another oxidizer may beprovided from a manifold outside the ring shaped arrangement through thestacks and the exit as a cathode exhaust stream to a manifold locatedinside the ring shaped arrangement). The side baffles 220 may alsoelectrically isolate the fuel cell stacks 14 from metal components inthe system. The load on the column 140 may be provided by thecompression assembly 600, which is held in place by the side baffles 220and the lower block 503. In other words, the compression assembly 600may bias the stacks 14 of the column 140 towards the lower block 503.

The side baffles 220 are plate-shaped rather than wedge-shaped andinclude baffle plates 202 and ceramic inserts 406 configured to connectthe baffle plates 202. In particular, the baffle plates 202 includegenerally circular cutouts 502 in which the inserts 406 are disposed.The inserts 406 do not completely fill the cutouts 502. The inserts 406are generally bowtie-shaped, but include flat edges 501 rather thanfully rounded edges. Thus, an empty space remains in the respectivecutouts 502 above or below the inserts 406.

The side baffles 220 and baffle plates 202 have two major surfaces andone or more (e.g., four) edge surfaces. One or more of the edge surfacesmay have an area at least 5 times smaller than each of the majorsurfaces. Alternatively, one or more edge surfaces may have an area atleast 4 times or 3 times smaller than at least one of the majorsurfaces. Preferably, the baffle plates 202 have a constant width orthickness, have a substantially rectangular shape when viewed from theside of the major surface, and have a cross sectional shape which issubstantially rectangular. In alternative embodiments, the ceramic sidebaffles 220 are not rectangular, but may have a wedge shapedcross-section. That is, one of the edge surfaces may be wider than theopposing edge surface. However, unlike the prior art baffles, whichcompletely fill the space between adjacent electrode stacks 14, the sidebaffles 220 of this embodiment are configured so that there is spacebetween side baffles 220. In other words, the side baffles 220 of thisembodiment do not completely fill the space between adjacent columns140. Wedge-shaped metal baffles may be inserted between adjacent sidebaffles 220, similar to the configuration shown in FIG. 1.

Generally, the side baffles 220 are made from a high-temperaturetolerant material, such as alumina or other suitable ceramic. In variousembodiments, the side baffles 220 are made from a ceramic matrixcomposite (CMC). The CMC may include, for example, a matrix of aluminumoxide (e.g., alumina), zirconium oxide or silicon carbide. Other matrixmaterials may be selected as well. The fibers may be made from alumina,carbon, silicon carbide, or any other suitable material. The lower block503 and the compression assembly 600 may also be made of the same orsimilar materials. The selection of particular materials for thecompression housing is discussed in detail, below.

Any combination of the matrix and fibers may be used. Additionally, thefibers may be coated with an interfacial layer designed to improve thefatigue properties of the CMC. If desired, the CMC baffles may be madefrom a unitary piece of CMC material rather than from individualinterlocking baffle plates. The CMC material may increase the bafflestrength and creep resistance. If the baffles are made from alumina oran alumina fiber/alumina matrix CMC, then this material is a relativelygood thermal conductor at typical SOFC operating temperatures (e.g.,above 700° C.). If thermal decoupling of neighboring stacks or columnsis desired, then the baffles can be made of a thermally insulatingceramic or CMC material.

Other elements of the compression housing, such as the lower block 503and the compression assembly 600 may also be made of the same or similarmaterials. For example, the lower block 503 may comprise a ceramicmaterial, such as alumina or CMC, which is separately attached (e.g., bythe inserts, dovetails or other implements) to the side baffles 220 andto a system base 239. The use of the ceramic block material minimizescreation of heat sinks and eliminates the problem of linking the ceramicbaffles to a metal base, which introduces thermal expansion interfaceproblems. The selection of particular materials for the components ofthe compression housing is discussed in detail, below.

FIG. 3 illustrates a fuel cell stack assembly 300 according to variousembodiments of the present disclosure. The fuel cell stack assembly 300is similar to the fuel cell stack assembly 200, so only the differencestherebetween will be discussed in detail. Similar elements have the samereference numbers. Fuel rails 214 (e.g. fuel inlet and outlet pipes orconduits) connect to fuel manifolds 204 located between the stacks 14 inthe column.

Referring to FIG. 3, the fuel cell stack assembly 300 includes sidebaffles 220 disposed on opposing sides of the column of fuel cell stacks14. However, each of the side baffles 220 includes only a single baffleplate 202, rather than the multiple baffle plates 202 of the fuel cellstack assembly 200. In addition, the side baffles 220 include ceramicinserts 406 to connect the baffle plates 202 to a compression assembly600 and a lower block 503.

FIG. 4 illustrates an embodiment of a compression assembly 600 that maybe used in conjunction with any of the embodiments described above.Referring to FIG. 4, the compression assembly 600 may be used to apply acompressive load to the column of fuel cell stacks 14. The compressionassembly 600 includes a spring 611. As illustrated, spring 611 is aceramic (e.g., CMC or alumina) leaf spring. A CMC spring is advantageousbecause it may include creep resistant fibers arranged in a direction inthe matrix which resists creep. The ceramic spring can exist in a hightemperature zone and allow for travel from differential thermalexpansion from components applying the load to the stack. However, anyother type of spring or combination of springs may be used. For example,the spring 611 may be a coil spring, a torsion spring, or a volutespring.

The compression assembly 600 may include a rod plate 607 configured toprovide a resilient surface against which the spring 611 can generate acompressive load. Preferably, the rod plate 607 includes retentionbarriers 608 configured to prevent the spring 611 from sliding off therod plate 607. When using a leaf spring, the rod plate 607 may alsoinclude spring support rods 604. In this configuration, the spring 611may be placed on top of the spring support rods 604 in an unstressedcondition (see also FIG. 5).

An upper plate 601 is provided on top of the spring 611, that is, on theopposite side of the spring 611 from the rod plate 607. The upper plate601 may include a spring tensioner 612, in this embodiment a rod, on thebottom of the upper plate 601. The spring tensioner 612 is preferablylocated approximately in the center of the upper plate 601. Thecompression assembly 600 may also be provided with an upper block 603which may include either cutouts 304 (which accept inserts 406 frombaffles as illustrated) or protrusions 303 by which compression assembly600 may be attached to the side baffles 220.

A temporary tightening mechanism may be attached over or to thecompression assembly 600 during the process of connecting the assemblyto the baffles 220. In the embodiment of FIG. 4, this mechanism includesa bracket 602. The bracket 602 may be affixed to the rod plate 607 bybolts as illustrated or by any other suitable mechanism. Movablyattached to the bracket 602 is a temporary tensioner which in thisembodiment comprises a pressure plate 605. As illustrated, the pressureplate 605 is movably attached to the bracket 602 by way of rods 609which slide in elongated slots 606.

The compression load applied by the compression assembly 600 may beadjusted via a pressure adjusting mechanism 610. The pressure adjustingmechanism 610 may be, for example, a screw or bolt which may be raisedor lowered by rotating. In the embodiment illustrated in FIG. 4,lowering the pressure adjusting mechanism 606 causes the pressure plate605 to travel downward. As the pressure plate 605 lowers, it forces theupper block 603 and the upper plate 601 to lower as well. When the upperplate 601 lowers, the spring tensioner 612 is forced against the centerof the spring 611, causing it to bend and thereby apply a load to thespring 611.

In use, the pressure adjusting mechanism 610 is lowered (and the spring611 compressed) until the upper block 603 can be connected (e.g.,hooked) to the side baffles 220. Once the side baffles 220 are connectedvia dovetails, inserts or other implements, the pressure adjustingmechanism 610 is loosened to release the bracket 602. The force of thespring 611, previously “held” by the pressure adjusting mechanism 610,is now transferred to the side baffles 220. Adjustment of thecompressive force on the stack may be attained by fitting shims (notshown) between the compression assembly 600 and the top of the column ofstacks 14 (which sits below the rod plate 607 of the compressionassembly 600). More shims create a tighter compression. The pressureadjusting mechanism 610 provides pretension to allow connection of thecompression assembly 600 to the side baffles 220. The bracket 602,including mechanism 610 and elements 605, 606 and 609 are then removedfrom the fuel cell column before the column is placed into an operatingmode.

FIG. 5 illustrates another embodiment of a compression assembly 600A.This embodiment is similar to the previous embodiment. However, the rodshaped spring tensioner 612 is replaced with a dome shaped springtensioner 612A, where the curved side of the dome is in contact with theupper surface of the spring. Spring support rods 604 contact edgeportions of a lower surface of the spring 611 to induce bending in thespring. Additionally, this embodiment includes spacers 702 which reducesthe distance between the block 603 and the spring 611, thereby reducingthe amount of adjustment required with the temporary tighteningmechanism, such as a bolt or screw (not shown for clarity) to apply aload to the spring 611 through opening 610A.

FIGS. 6A and 6B illustrate are schematic views of a fuel cell stackassembly, which may be any of the above-described fuel cell stackassemblies 200, 300, or another type of fuel cell stack assembly, at 20°C. and 700° C., respectively. Referring to FIGS. 6A and 6B, thecoefficient of thermal expansion (CTE) of the column 140 of fuel cellstacks may be different from the CTE of the side baffles 220. Forexample, the CTE of the column 140 may be about 9.7, at roomtemperature. The CTE of the side baffles 220 may about 7.2 at roomtemperature, if the side baffles 220 are formed of about 99 wt %alumina. Accordingly, as shown in FIGS. 6A and 6B, as the fuel cellstack assembly is heated, the column 140 expands faster than the sidebaffles, resulting in increased deflection of the compression assembly600. As such, the load applied to the column 140 is increased. Althoughcompression assembly 600 is shown, any other suitable compressionassemblies may be used.

It is also important to note that the spring constant of the compressionassembly may be highly non-linear. Further, since the compressionassembly is already deflected at 20° C., the additional deflection at700° C. may apply a substantially higher load to the column 140. Basedon modeling, it is calculated that an original load of 350 lbs at roomtemperature can exceed 1000 lbs, when the column 140 heats up to 650° C.(before the interface seals melt). The opposite scenario is also true,in that the load on the column 140 will be reduced significantly, if thecolumn 140 is cooled from a high temperature. The fundamental reason forthis difference is the CTE difference between the column 140 and theside baffles. The increased loading at high temperatures may result indamage to the fuel cell stacks of the column 140 and/or other componentsof the fuel cell stack assembly.

In order to overcome or reduce the above and/or other problems, the sidebaffles 220 of the above embodiments may be configured to have a CTEthat is substantially the same (within about +/−20%, such as +/−10%) asthe CTE of the column 140. According to some embodiments, the CTE of thebaffle plates 202 may be within about +/−5% of the CTE of the column140. The CTE of the side baffles may be altered by altering thecomposition of one or more components of the side baffles 220. Herein,the CTE of an element refers to a CTE of the element at roomtemperature.

For example, when the side baffles each include a single baffle plate202, as shown in the embodiment of FIG. 3, the baffle plates 202 can beformed of a material having a CTE that is similar to the CTE of thecolumn 140. In particular, the CTE of the baffle plates 202 may bewithin about +/−20%, such as +/−10% of the CTE of the fuel cell stack.The CTE of the baffle plates 202 may be controlled by doping or mixingalumina with other ceramic components, or by choosing different materialsets. The following Table 1 includes exemplary ceramic materials thatmay be included in the side baffles and corresponding CTE's. However,the present disclosure is not limited to such materials, as othersuitable materials may be used.

TABLE 1 Material CTE (Room Temperature) Alumina 7.2 Zirconia(Tetragonal) 12 Magnesia 13.5 Alumina-Titania Mixture 9.7Zirconia-Magnesia Mixture 12

As shown in Table 1, an alumina-titania mixture may be prepared to havea CTE of 9.7, which is substantially the same as the CTE of a column offuel cell stacks. As such, a side baffle 220 including analumina-titania mixture expands at substantially the same rate as thecolumn 140, which prevents excessive loading of the column 140 duringheating.

Further, zirconia (tetragonal phase), magnesia, and a zirconia-magnesiamixture exhibit CTE's that are slightly higher than 9.7. As such, sidebaffles 220 including these materials could also prevent excessiveloading of the column 140 during heating. While these materials wouldexpand at a higher rate than the column 140, such a difference can becompensated for by a compression assembly, since the spring constant ofthe compression assembly 600 may be more linear at lower levels ofcompression. Side baffles 220 can include a mixture of alumina andmagnesia, or a mixture of alumina and zirconia, with amount ratios ofthe mixtures configured such that the side baffles 220 and the column140 have substantially the same CTE.

The baffle plates 202 and the ceramic inserts 406 of the side baffles220 may be formed of the same material. However, according to someembodiments, the baffle plates 202 and the ceramic inserts 406 may beformed of different materials that have CTE's that are higher or lowerthan the CTE of the column 140, so long as the total CTE of the sidebaffles 220 is similar to the CTE of the column 140.

FIG. 7 is a schematic view of a fuel cell stack assembly 200A, accordingto various embodiments of the present disclosure. The assembly 200A maybe similar to the assembly 200 or 300 described above. Referring to FIG.7, the fuel cell stack assembly 200A includes side baffles 220, an upperblock 603, a compression assembly 600, a lower block 503, and a fuelcell stack column 140. The column 140 includes fuel cell stacks 14 thatmay include stacked fuel cells 18, interconnects 17 separating the fuelcells 18, fuel manifolds 204 (anode splitter plates), end plates 25, andtermination plates 27. The termination plates 27 may be disposed atopposing ends of the column 140. The fuel cells 18 may be solid oxidefuel cells. The end plates 25 may be disposed on opposing ends of thefuel cell stacks 14. The end plates 25 may be disposed between thetermination plates 27 and the adjacent fuel cells 18 at opposing ends ofthe column 140. The fuel manifolds 204 may be disposed between the fuelcell stacks 14.

According to some embodiments, the interconnects 17 and the end plates25 may be made of a Cr—Fe alloy with a CTE of about 9.7 ppm/° C. Forexample, the chromium-iron alloy may include, by weight, from about 94to about 95%, such as about 95% Cr, and from about 4 to about 6%, suchas about 5% Fe. The termination plates 27 and the fuel manifolds 204 maybe made of a ferritic stainless steel having a CTE between about 10.4and 12.1 ppm/° C. For example, the ferritic stainless steel may be SS446, which may include, by weight, 23.0%-27.0% Cr, 1.5% Mn, 1.0% Si,0.25% Ni, 0.20% Ni, 0.20% C, 0.04% P, and 0.03% S and balance Fe (e.g.,73% Fe).

The present inventors determined that there is a high propensity for thefuel cells 18 at ends of the stacks 14 to develop cracks after thermalcycling. However, the present inventors further determined that if thetermination plates 27 are formed by powder metallurgy using the Cr—Fealloy with a nearly identical CTE as the end plates 25, rather thanstainless steel, the likelihood of cracking the end fuel cells 18 isdecreased significantly. Without wishing to be bound to a particulartheory, the present inventors believe that the CTE mismatch between theend plates 25 and the fuel manifolds 204 or termination plates 27 mayresult in fuel cell cracking during thermal cycling. In response, thetermination plates 27 and the fuel manifolds 204 of the followingembodiments have been configured to reduce the stresses resulting fromthe thermal expansion differences described above.

FIG. 8A is a plan view of a modified termination plate 27 according tovarious embodiments of the present disclosure, and FIG. 8B is a planview of a general termination plate 27G of a comparative example.Referring to FIGS. 8A and 8B, the termination plates 27, 27G includeterminals 29 configured to electrically connect a fuel cell stack to apower conditioning module using attached electrical wires, jumpers, orother suitable electrical connectors, and sealing surfaces 31 configuredto seal fuel riser openings of adjacent end plates 25. The generaltermination plate 27G includes a single main body 33.

In contrast, the modified termination plate 27 includes a main bodydivided into first and second separate pieces 33A, 33B. According tosome embodiments, the first and second pieces 33A, 33B may be separatedby an expansion zone 33C, which is similar to the expansion zone 221Cdescribed below. Each piece 33A, 33B includes a fuel riser openingsealing surface 31, which may be configured to seal the fuel riseropening of an adjacent stack component (e.g., of adjacent end plates).The terminal 29 is shown as being connected the second piece 33B.However, the terminal 29 may be connected to the first piece 33A in someembodiments.

With this design, the sealing surfaces 31 of each piece 33A, 33B arefree to float with respect to each other, due to the segmentation of themain body. This design also allows for the relative displacement of thetermination plate pieces 33A, 33B when coupled to an end plate having adifferent CTE, and for the relative displacement of the sealing surfaces31, thereby reducing stresses applied to adjacent fuel cells andreducing fuel cell cracking during thermal cycling.

FIG. 9 is an exploded perspective view of a portion of a fuel cell stackassembly 200B, according to various embodiments of the presentdisclosure. The fuel cell stack assembly 200B is similar to the fuelcell stack assembly 200A, so only the differences therebetween will bediscussed in detail.

Referring to FIG. 9, the fuel cell stack assembly 200B includes fuelcell stacks 14 and a fuel manifold 204A. The fuel manifold 204A includesfirst and second fuel conduits 214A, 214B (e.g., rail shaped pipes),first and second fuel holes (i.e., fuel riser openings through themanifold) 219A, 219B, fuel hole seals 223, and a main body 221 includingfirst and second separate pieces 221A, 221B. According to someembodiments, the first and second pieces 221A, 221B may be separated byan expansion zone 221C. The expansion zone may be an empty space betweenpieces 221A and 221B, a sealing material filled space or the interfacewhere the sidewalls of the first and second pieces contact each other.If the sidewalls of the pieces contact each other, there is preferablynot connection between the pieces across the expansion zone 221C toallow the pieces to “float” independent of each other. The first fuelconduit 214A is connected to the first fuel hole 219A through the firstpiece 221A. The second fuel conduit 214B is connected to the second fuelhole 219B through the second piece 221B. In operation, fuel may flowfrom the first conduit 214A (e.g., fuel inlet conduit), through thefirst piece 221A, and then out of the first fuel hole 219A. The fuel maybe circulated in the stacks 14 before becoming a fuel exhaust whichenters the second fuel hole 219B, flowing through the second piece 221B,and then into the second conduit 214B (e.g., the fuel exhaust conduit).In particular, the first and second pieces 221A, 221B may be hollow ormay include conduits connecting the respective conduits 214A, 214B andthe fuel holes 219A, 219B. According to other embodiments, the fuel mayflow in the opposite direction through the fuel cell stack assembly 200B(i.e., where conduit 214B is the fuel inlet conduit and conduit 214A isthe fuel exhaust conduit).

The segmentation of the main body 221 allows the first and second pieces221A, 221B to float relative to one another. Accordingly, stressesapplied to adjacent fuel cell stack components, such as end plates andfuel cells, may be reduced during thermal cycling. While the fuelmanifold 204A is shown to include an L-shaped first piece 221A and agenerally rectangular second piece 221B, the present disclosure is notlimited thereto. In particular, the pieces 221A, 221B may have otherconfigurations, so long as each fuel hole and is connected to a fuelriser conduit or channel through a respective piece of the main body.According to some embodiments, the assembly 200B may include thetermination plate 27 of FIG. 8A, or the termination plate 27G of FIG.8B.

FIG. 10 is an exploded perspective view of a fuel cell stack assembly200C, according to various embodiments of the present disclosure. Thefuel cell stack assembly 200C is similar to the fuel cell stack assembly200A, so only the differences therebetween will be discussed in detail.

Referring to FIG. 10, the fuel cell stack assembly 200C includes a fuelcell stack 14, a fuel manifold 204, a buffer layer 225 including fuelriser openings 229 (e.g., inlet and outlet openings), first seals 231and second seals 233. The buffer layer 225 includes a material having aCTE between that of the fuel manifold 204 an adjacent component of thestack 14, such as an end plate 25 (e.g., Cr—Fe alloy plate). In someembodiments, buffer layers 225 may be disposed between any components ofthe stack that have a CTE mismatch, as discussed below with reference toFIG. 11.

The first seals 231 may be disposed between the buffer layer 225 and thestack 14 and may operate to seal the riser openings 229. The first seals231 may include a glassy (e.g., glass) material. The second seals 233may be disposed between the buffer layer 225 and the fuel manifold 204and may operate to seal the riser openings 229 and the fuel holes 219Aand 219B in the manifold 204. The second seals 233 may include acompliant material, such as felt or mica. The second seals 233 may alsoinclude felt or mica in combination with a glassy material. In otherembodiments, the second seals 233 may include a metal gasket. The firstand/or second seals 231, 233 may operate to reduce stress applied tofuel cell components during thermal cycling.

FIG. 11 is a schematic view of a fuel cell stack assembly 200D,according to various embodiments of the present disclosure. The fuelcell stack assembly 200D is similar to the fuel cell stack assembly200A, so only the differences therebetween will be discussed in detail.

Referring to FIG. 11, the fuel cell stack assembly 200D includes bufferlayers 225 disposed between various components. For example, bufferlayers 225 may be disposed between the termination plates 27 and theadjacent end plates 25 of adjacent stacks. In addition, buffer layers225 may be disposed between the fuel manifolds 204 and adjacent endplates 25. According to some embodiments, one or more of the bufferlayers 225 may be omitted.

The buffer layer 225 may be configured to minimize the stress applied toadjacent components of the stack 14. Therefore, in some embodiments, theCTE of the end plate 25 is less than the CTE of buffer layer 225, andthe CTE of the buffer layer 220 is less than the CTE of the fuelmanifold 204 and/or termination plate 27. In other embodiments, the CTEof the end plate 25 may be higher than the CTE of the buffer layer 225,and the CTE of the buffer layer 225 may be higher than the CTE of thefuel manifold 204 and/or the termination plate 27.

One material suitable for use in the buffer layer 225 is a ferriticstainless steel-aluminum oxide cermet, such as SS446-Al₂O₃, which isstable at high temperatures. The CTE of such a material can be tailoreddepending of the amount of added Al₂O₃. SS446 stainless steel may have acomposition of 23-27 wt % Cr, 1.5 wt % Mn, 1 wt % Si, 0.25 wt % Ni, lessthan 1 wt % C, P and S, and balance iron. This cermet material iscastable, so plates can be readily and inexpensively produced. Anothersuitable material may be Inconel 783. The Inconel 783 is an alloyincluding 26-30 wt % Ni, 24-27 wt. % Fe, 5-6 wt. % Al, 2.5-3.5 wt. % Cr,2.5-3.5 wt. % Nb, up to 0.50 wt. % Cu, up to 0.50 wt. % Mn, up to 0.50wt. % Si, up to 0.10-0.40 wt. % Ti, up to 0.03 wt. % C, 0.003-0.012 wt.% B, up to 0.015 wt. % P, up to 0.005 wt. % S, and balance Co. Otherelectrically conductive cermet or metal alloy materials having a CTE ofgreater than 9.7 and less than 10.4 ppm/° C. may also be used.

FIG. 12 is an exploded perspective view of a fuel cell stack assembly200E, according to various embodiments of the present disclosure. Thefuel cell stack assembly 200E is similar to the fuel cell stack assembly200C, so only the differences therebetween will be discussed in detail.

Referring to FIG. 12, the fuel cell stack assembly 200E includes abuffer layer 227 having a segmented configuration. In particular, thebuffer layer 227 includes a first piece 227A and a second piece 227B,each including a fuel riser opening 229. According to some embodiments,the first and second pieces 227A, 227B may be separated by an expansionzone 227C. The division of the buffer layer 227 reduces stress appliedto fuel cell assembly components resulting from CTE mismatch of fuelcell stack assembly components.

Any one or more features from any one or more embodiments may be used inany suitable combination with any one or more features from one or moreof the other embodiments. Although the foregoing refers to particularpreferred embodiments, it will be understood that the invention is notso limited. It will occur to those of ordinary skill in the art thatvarious modifications may be made to the disclosed embodiments and thatsuch modifications are intended to be within the scope of the invention.All of the publications, patent applications and patents cited hereinare incorporated herein by reference in their entirety.

What is claimed is:
 1. A fuel cell stack column comprising: first andsecond termination plates; and at least one fuel cell stack disposedbetween the first and second termination plates, wherein at least one ofthe first and second termination plates comprises first and secondpieces separated by an expansion zone.
 2. The fuel cell stack column ofclaim 1, wherein each of the first and second pieces comprises a fuelriser opening sealing surface.
 3. The fuel cell stack column of claim 1,wherein the first and second the termination plates comprise electricalconnectors attached to one of the corresponding first and second pieces.4. The fuel cell stack column of claim 1, wherein the fuel cell stackcolumn comprises a plurality of the fuel cell stacks and fuel manifoldsdisposed between the fuel cell stacks, each fuel cell stack comprising:fuel cells; interconnects disposed between the fuel cells; and endplates disposed on opposing sides of the fuel cell stack, wherein thecoefficient of thermal expansion (CTE) of the fuel cell stack is notequal to the CTE of the termination plates.
 5. The fuel cell stackcolumn of claim 4, wherein the fuel manifolds each comprise first andsecond pieces separated by an expansion zone.
 6. The fuel cell stackcolumn of claim 5, further comprising: a first buffer layers disposedbetween the fuel manifolds and an adjacent fuel cell stack; and a secondbuffer layers disposed between the termination plates and the adjacentfuel cell stacks, wherein the first and second buffer layers eachcomprise first and second pieces separated by an expansion zone.
 7. Afuel cell stack column comprising: first and second fuel cell stacks;and a fuel manifold comprising a main body disposed between the firstand second fuel cell stacks, the main body comprising first and secondpieces separated by an expansion zone.
 8. The fuel cell stack column ofclaim 7, wherein: the fuel manifold comprises first and second fuelconduits respectively disposed on the first and second pieces of themain body; and the first and second pieces comprises fuel riser openingsthat are respectively fluidly connected to the first and second fuelconduits and to respective inlet and exhaust risers of the first andsecond stacks.
 9. The fuel cell stack column of claim 7, wherein thecoefficient of thermal expansion (CTE) of the first and second fuel cellstacks is not equal to the CTE of the fuel manifold.
 10. The fuel cellstack column of claim 7, further comprising first and second terminationplates, wherein the first and the second fuel cell stacks are disposedbetween the first and second termination plates, and wherein at leastone of the first and second termination plates comprises first andsecond pieces separated by an expansion zone.
 11. The fuel cell stackcolumn of claim 7, further comprising buffer layers disposed between thefuel manifold and the first and the second fuel cell stacks, wherein thebuffer layers each comprise first and second pieces separated by anexpansion zone.
 12. A fuel cell stack column comprising: terminationplates; fuel cell stacks disposed between the termination plates, eachfuel cell stack comprising: fuel cells; interconnects disposed betweenthe fuel cells; and end plates disposed on opposing ends of the fuelcell stack; a fuel manifold comprising a main body disposed between atleast two adjacent fuel cell stacks; and at least one of: a first bufferlayer disposed between the fuel manifold and an adjacent fuel cellstack; and a second buffer layer disposed between one of the terminationplates and the adjacent fuel cell stack; wherein: a coefficient ofthermal expansion (CTE) of the first buffer layer is between the CTE ofthe end plates and the CTE of the fuel manifold, and the CTE of thesecond buffer layer is between the CTE of the end plates and the CTE ofthe termination plates.
 13. The fuel cell stack column of claim 12,wherein the at least one of the first and second buffer layers comprisesa ferritic stainless steel-aluminum oxide cermet.
 14. The fuel cellstack column of claim 12, wherein the at least one of the first andsecond buffer layers comprises Inconel
 783. 15. The fuel cell stackcolumn of claim 12, wherein the at least one of the first and secondbuffer layers comprises first and second pieces separated by anexpansion zone.
 16. The fuel cell stack column of claim 15, wherein eachof the first and second pieces of the at least one buffer layercomprises a fuel riser opening.
 17. The fuel cell stack column of claim12, further comprising a first seal disposed between the first bufferlayer and an adjacent end plate; and a second seal disposed between thefirst buffer layer and an adjacent fuel manifold; wherein: the firstseal comprises a glassy material; and the second seal comprises acompliant material selected from felt, mica or a combination of felt ormica and a glassy material.
 18. The fuel cell stack column of claim 12,wherein the coefficient of thermal expansion (CTE) of at least one ofthe first and second buffer layers ranges from about 9.7 to about 10.4ppm/° C.
 19. The fuel cell stack column of claim 12, wherein: at leastone of the termination plates comprises first and second piecesseparated by an expansion zone; and the fuel manifold comprises firstand second pieces separated by an expansion zone.
 20. The fuel cellstack column of claim 12, wherein: the fuel cells comprise solid oxidefuel cells; the interconnects comprise a Cr—Fe alloy; the terminationplates comprise SS 446; the fuel manifold comprises SS
 446. 21. The fuelcell stack column of claim 12, wherein: a coefficient of thermalexpansion (CTE) of the first buffer layer is greater than the CTE of theend plates and is less than the CTE of the fuel manifold; and the CTE ofthe second buffer layer is greater than the CTE of the end plates and isless than the CTE of the termination plates.
 22. The fuel cell stackcolumn of claim 12, wherein: a coefficient of thermal expansion (CTE) ofthe first buffer layer is less than the CTE of the end plates and isgreater than the CTE of the fuel manifold; and the CTE of the secondbuffer layer is less than the CTE of the end plates and is greater thanthe CTE of the termination plates.